BENEFITS OF THERMAL TREATMENT OF WASTEWATER & SLUDGE IN VARIOUS AREAS OF E/M SPECTRUM

Ενώ η θερμική επεξεργασία των υγρών αποβλήτων με Υπέρυθρη Ακτινοβολία (ΥΑ), Μικροκυματική Ακτινοβολία (ΜΑ) και Ραδιοσυχνότητες – Διηλεκτρική Θέρμανση (ΡΣ – ΔΘ) είναι δυνατή για βιομηχανική χρήση για διάστημα πλέον των 60 ετών, η πραγματική χρήση της είναι περιορισμένη, για την επεξεργασία δε της λυματολάσπης έχουν γίνει μόνο σποραδικές προσπάθειες. Ωστόσο, η επεξεργασία αυτή φαίνεται να προσφέρει μοναδικά οφέλη και αναμένεται να συγκεντρώσει το ενδιαφέρον της επιστημονικής / τεχνικής κοινότητας τα επόμενα έτη. Όταν εφαρμόζεται σωστά, μπορεί να βελτιώσει σημαντικά την κερδοφορία της βιομηχανικής επεξεργασίας λυματολάσπης κατά τρόπο που δεν επιτυγχάνεται με τις συμβατικές μεθόδους.While heat treatment of wastewaters with infrared radiation, microwaves and radio frequencies is available for industrial use for more than 60 years, its actual use is limited, while only sporadic efforts have been made for the management of sludge. However, this treatment option seems to offer unique benefits and will attract the interest of the scientific / technical community in the coming years. When properly applied, it can significantly improve the profitability of industrial sludge treatment in a way that is not achieved by any other means

A Review of the Carbon Footprint of Cu and Zn Production from Primary and Secondary Sources

Copper (Cu) and zinc (Zn) with their unique properties are central for economic growth, quality of life, and the creation of new jobs. The base-metal producing sector is, however, under growing public pressure in respect to energy and water requirements and needs to meet several challenges, including increased demand and lower ore grades, which are generally associated with larger resource use. The development of technologies for metal production from secondary sources is often motivated by increased sustainability, and this paper aims to provide further insights about one specific aspect of sustainability—namely, climate change. The paper presents a review of carbon footprints (CF) for Cu and Zn produced from primary and secondary raw materials by analyzing data taken from scientific literature and the Ecoinvent database. Comparisons are carried out based on the source of data selected as a reference case. The data available in the literature indicate that secondary production of Cu and Zn has the potential to be more beneficial compared to primary production regarding the impact on climate change. However, the technologies used today for the production of both metals from secondary sources are still immature, and more research on this topic is needed. The general variation of data suggests that the standardization of a comparison is needed when assessing the environmental benefits of production in line with the principles of waste valorization, the zero waste approach, and circular econom

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zincrich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account

Adsorption of Scandium and Neodymium on Biochar Derived after Low-Temperature Pyrolysis of Sawdust

The objective of this study was to investigate the adsorption of two rare earth elements (REEs), namely scandium (Sc) and neodymium (Nd), on biochar produced after low temperature pyrolysis (350 °C) of wood sawdust. The biochar was characterized with the use of several analytical techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric (TG) analysis, while the pH at point of zero charge (pHPZC) was also determined. The experimental conditions were: absorbent concentration 1–10 g·L−1, REE concentration in solution 20 mg·L−1, contact time for equilibrium 24 h, temperature 25 °C and stirring speed 350 rpm. The efficiency of biochar was compared to that of a commercial activated carbon. Geochemical modelling was carried out to determine speciation of Nd and Sc species in aqueous solutions using PHREEQC-3 equipped with the llnl database. The experimental results indicated the potential of low temperature produced biochar, even though inferior to that of activated carbon, to adsorb efficiently both REEs. The equilibrium adsorption data were very well fitted into the Freundlich isotherm model, while kinetic data suggested that the removal of both REEs follows the pseudo-second order kinetic reaction. Finally, the most probable adsorption mechanisms are discussed

Social License to Operate in Mining: Present Views and Future Trends

The social license to operate (SLO) is an informal social contract that aims to bridge the gap among the views of the most important stakeholders involved in mining activities. The novelty of this paper lies in the fact that it discusses the current situation and the future prospects of granting a SLO, mainly at the European Union (EU) level, by considering the mine of the future, in terms of deep sea and landfill mining, and the criticality of raw materials that are required by high tech products as well as by emerging and green technologies. Also, it highlights the factors that may affect the views of all involved stakeholders, focusing on the joint efforts that are required by the industry and the society as well as on the main technological, social, political and legal issues which are relevant to the process. It is believed that if trust is developed between the involved stakeholders the SLO may prove an important tool in future mining in order to safeguard the supply of raw materials, minimize the environmental footprint and improve the quality of life in the affected regions. Finally, a conceptual flowsheet involving the main steps that may be followed for granting a SLO is proposed

Improved Modeling of the Grinding Process through the Combined Use of Matrix and Population Balance Models

The mechanistic approach has proven so far to be flexible and successful for simulation of the grinding process. The basic idea underlying mechanistic models, namely the matrix and population balance models, is based on the identification of natural events during grinding. Since each model has its own capabilities and limitations, their combined use may offer additional advantages on this aspect. In this study, the matrix model and the selection function, namely the probability of breakage of the population balance model, were combined through a MATLAB code to predict the size distribution of the grinding products of quartz, marble, quartzite and metasandstone. The modeling results were in very good agreement with the particle size distributions obtained after grinding the feeds in a ball mill

Effect of Grinding Media Size on Ferronickel Slag Ball Milling Efficiency and Energy Requirements Using Kinetics and Attainable Region Approaches

The aim of this study is to evaluate the effect that the size of grinding media exerts on ferronickel slag milling efficiency and energy savings. A series of tests were performed in a laboratory ball mill using (i) three loads of single size media, i.e., 40, 25.4, and 12.7 mm and (ii) a mixed load of balls with varying sizes. In order to simulate the industrial ball milling operation, the feed to the mill consisted of slag with natural size distribution less than 850 μm. Grinding kinetic modeling and the attainable region (AR) approach were used as tools to evaluate the data obtained during the ball milling of slag. Particular importance was given to the determination of the specific surface area of the grinding products, the identification of the grinding limit, and the maximum specific surface area which could be achieved when different grinding media sizes were used. The results showed that, in general, the breakage rates of particles obey non-first-order kinetics and coarse particles are ground more efficiently than fines. The AR approach proved that there is an optimal grinding time (or specific energy input) dependent on the ball size used for which the volume fraction of the desired size class is maximized. The use of either 25.4 mm balls or a mixed load of balls with varying sizes results in 31 and 24% decrease in energy requirements, compared to the use of balls with small size (12.7 mm)

Effect of Grinding Media Size on Ferronickel Slag Ball Milling Efficiency and Energy Requirements Using Kinetics and Attainable Region Approaches

The aim of this study is to evaluate the effect that the size of grinding media exerts on ferronickel slag milling efficiency and energy savings. A series of tests were performed in a laboratory ball mill using (i) three loads of single size media, i.e., 40, 25.4, and 12.7 mm and (ii) a mixed load of balls with varying sizes. In order to simulate the industrial ball milling operation, the feed to the mill consisted of slag with natural size distribution less than 850 μm. Grinding kinetic modeling and the attainable region (AR) approach were used as tools to evaluate the data obtained during the ball milling of slag. Particular importance was given to the determination of the specific surface area of the grinding products, the identification of the grinding limit, and the maximum specific surface area which could be achieved when different grinding media sizes were used. The results showed that, in general, the breakage rates of particles obey non-first-order kinetics and coarse particles are ground more efficiently than fines. The AR approach proved that there is an optimal grinding time (or specific energy input) dependent on the ball size used for which the volume fraction of the desired size class is maximized. The use of either 25.4 mm balls or a mixed load of balls with varying sizes results in 31 and 24% decrease in energy requirements, compared to the use of balls with small size (12.7 mm)

Correlation between Material Properties and Breakage Rate Parameters Determined from Grinding Tests

The present study investigates four materials, namely quartz, marble, quartzite and metasandstone and aims to establish correlations, with the use of simple and multiple regression analysis, between their properties and breakage rate parameters. The material properties considered in this study derived from the application of destructive and non-destructive tests and include P-wave velocity (Vp), Schmidt rebound value (RL), uniaxial compressive strength (UCS) and tangent modulus of elasticity (Et), while the breakage rate parameters determined from batch grinding tests, include breakage rate Si, maximum breakage rate Sm, αT and α, and optimum particle size xm. The results indicate that the properties of all materials examined show very good correlation and can be used to predict Si or αT. Furthermore, parameter α is well correlated with Vp, RL and Et using inverse exponential functions, while Sm is strongly correlated with RL and UCS. Overall, it is deduced that multiple regression analysis involving two independent variables is a reliable approach and can be used to identify correlations between properties and breakage rate parameters for quartz, quartzite and metasandstone, which are silica rich materials. The only exception shown is the determination of xm for marble